I have a XPS 13 9370 with the same card and I'm seeing exactly the same. My card was being detected correctly in Ubuntu 18.04 but stopped being detected when I upgraded to the Ubuntu 18.10 development version.

I'm on this for more than two hours. Everything I try just fails, and every search I attempt results into outdated or non-working tips. I was able to get sound by adding myself to the audio group; now speaker-test -D sysdefault:CARD=PCH works, but PulseAudio stubbornly does not detect my device. Tried to delete ~/.config/pulse, tried to restart PulseAudio, attempted to get verbose logging, no useful information. pactl list and pavucontrol only show a NVIDIA HDMI audio, and a USB webcam, no onboard HDA Intel. Do I really need to get an external USB sound card for Ubuntu 18.10? This is a real deal breaker. We need a downgrade path if upgrade fails the system that hard, but there is no such thing, besides formatting and loosing all my settings.

I ended up running sudo apt purge pulseaudio, which completely removed PulseAudio and some configuration files. Then I rebooted and surprise, sound was back. However, it wasn't working for Firefox/YouTube, and Spotify. I then tried to reinstall PulseAudio, which didn't do anything. But systemctl --user start pulseaudio restarted the daemon, and then I have sound. I tried to reboot and still have sound.
Not sure if that will remain stable, will have to monitor this.

There are at least two issues: I got removed from the "audio" group which prevented me from using ALSA devices, then PulseAudio configuration got screwed up preventing PulseAudio from accessing ALSA devices.